Field of the Invention
This invention relates to a method for making manganese oxide media that can be used in chemical processes and to treat organic contaminated materials, and to a method of treating organic contaminated materials.
Technical Considerations
Many environmental operations result in the production of contaminated materials, such as contaminated water, which must be treated or otherwise decontaminated before being released back into the environment. An example of one such operation is conventional coal mining, which can result in the production of drainage containing dissolved metal contaminants, such as manganese, iron, and aluminum.
Manganese is a common water contaminant that is most frequently treated by the addition of chemicals. The addition of chemicals promotes the oxidation of manganese (II) (Mn2+) to manganese dioxide and oxyhydroxide minerals through pH adjustment (such as adding sodium hydroxide or calcium oxide) or oxidant addition (such as adding potassium permanganate or ozone). The chemical treatment of manganese contaminated water results in the formation of a low-density, chemically-diverse sludge that must be managed (i.e., collected and disposed of) at significant cost. An alternative treatment process involves the passive treatment of manganese contaminated coal mine drainage without the addition of chemicals. For example, manganese (II)-contaminated water is directed through a bed of aggregate, such as loose pieces of rocks or gravel. Reactions on the aggregate surfaces promote the formation of a layer of manganese oxide(s) on the aggregate surfaces. The process has both abiotic and biotic components. Additional manganese (II) in the contaminated water is adsorbed onto the previously formed manganese oxide layer on the aggregate and is oxidized to manganese oxide, thus increasing the thickness of the manganese oxide layer on the aggregate. Bacteria and fungi associated with the media promote the oxidation of manganese (II) through metabolic activities. Manganese oxide produced by a combination of biological and chemical processes is sometimes referred to as Biogenic Manganese Oxide (or BioMnOx). For acidic waters, the use of calcareous limestone aggregate is common because of its acid neutralizing capabilities. In cases where the water is naturally alkaline or limestone is not available, non-calcareous aggregate may be utilized.
The most common use of passive treatment for the removal of dissolved manganese from contaminated water is in the coalfields of the eastern U.S., where dozens of treatment systems have been constructed over the last twenty years. In these treatment systems, coal mine drainage flows through a bed of aggregate. These systems function through the precipitation of dissolved manganese onto the aggregate surfaces to form a coating layer of manganese oxide on the aggregate surfaces. Eventually, the accumulation of manganese oxide on the surfaces of the aggregate decreases the porosity of the aggregate bed to a point where its effectiveness is diminished. To maintain the effectiveness, the aggregate must be periodically cleaned or replaced with fresh aggregate. In both cases, wastes are generated that must be disposed of.
Manganese oxide minerals are recognized as potent remedial agents because of their strong oxidative capacities. The oxidative decomposition of a simple organic compound is generalized by the following reaction:2MnO2+CH2O+4H+→2Mn2++CO2+3H2O  Formula I
As shown in Formula I, manganese dioxide (MnO2) is reduced to manganese (II) (Mn2+) while an organic compound, represented by “CH2O”, is oxidized to carbon dioxide (CO2).
Manganese oxide has been shown to oxidize and decompose a large variety of organic contaminants. Examples of such contaminants include antimicrobial agents, chelating agents, dyes, endocrine disruptors, flame retardants, pesticides, and various pharmaceutical agents including atrazine, glyphosate, ciprofloxacin, sulfadiazine, triclosan, chlorophene, fluoroquinolone, phenols, aromatic N-oxide, tetracyclines, lincosamides, macrolide, chlorophene, sulfonamide, Tetracycline, chlortetracycline, methylene blue, Bisphenol A, Bisphenol F, steroid estrogens, 17β-Estradiol, tetrabromobisphenol A, 2-mercaptobenzothiazole (MBT), carbamazepine, diclofenac, nonylphenol (NP), octylphenol (OP), 17a-ethinylestradiol, and many pharmaceuticals.
The use of manganese oxide for the treatment of organic contamination typically is accomplished by adding chemically-prepared manganese oxide to the contaminated water. The manganese oxide may be pure manganese oxide minerals or sand particles that have been coated with manganese oxide by a chemical precipitation process. The effectiveness of the treatment decreases as manganese (II) accumulates in solution and adsorbs preferentially onto manganese oxide, lessening the organic oxidative capabilities. These chemical treatment procedures do not include a means to reoxidize the released manganese (II) to manganese oxide in order to sustain the oxidative process.
Therefore, it would be desirable to devise a treatment system for organic contaminants that does not generate waste and which can be self-sustaining.